This invention is concerned with the production of a substitute natural gas derived from carbonaceous feedstocks, in particular crude petroleum or distillate fractions produced therefrom, but which may also be residual oil fractions and other hydrocarbons. Normally when the feedstock is hydrogenated at an elevated temperature with commercially-produced hydrogenating gas, to which steam may or may not be added, the resulting gaseous mixture normally contains, beside hydrocarbons, carbon oxides and untreated hydrogen which detract from the reaction products being ideally suitable as a substitute for natural gas.